1. Field of the Invention
The present invention relates to a vane pump for compressing fluid.
2. Description of Related Art
An example of a vane pump having a rotor rotating in an eccentric relation with respect to an inner bore of a casing is disclosed in JP-A-2003-222089. The rotor rotates in the inner bore of the casing at a high speed. If there is dimensional errors in the housing and the rotor, or there is an inclination in coupling the rotor with a driving shaft, it is possible that the rotor contacts the inner bore of the casing. If this happens, noises will be generated, and the rotor and the casing will be damaged by abrasion. In the worst case, the rotor will be locked. Further, the rotor may be deformed in a process of press-fitting the driving shaft into the rotor.
In order to avoid these troubles, all the components of the vane pump, i.e., the driving shaft, the rotor and the casing have to be machined with a high precision. Alternatively, it would be preferable to loosely couple the driving shaft to the rotor with a certain gap therebetween to absorb dimensional errors. However, if there is a gap between the driving shaft and the rotor, the rotor vibrates relative to the driving shaft when it is rotated, generating noises and making compression pressure unstable.